| 摘要 |
Differential pressures across flow control valves 6a, 6b and 6c are controlled by pressure compensating valves 7a, 7b and 7c to be held at the same value, i.e., a differential pressure DELTAPLS, and the differential pressure DELTAPLS is maintained at a target differential pressure DELTAPLSref by a pump displacement control unit 5. For changing the target differential pressure depending on change in revolution speed of an engine 1, a flow detecting valve 31 is disposed in a delivery line 30a, 30b of a fixed displacement hydraulic pump 30, and a differential pressure DELTAPp across a variable throttle portion 31a of the flow detecting valve 31 is introduced to a setting controller 32. A selector valve 50 operable to shift between a fully closed position and a throttle position is disposed in parallel to the flow detecting valve 31 and is shifted by a control lever 51. With that arrangement, the target differential pressure in load sensing control can be changed depending on the revolution speed of a prime mover. Also, even when a change width of the demanded actuator speed exceeds the range adjustable with the revolution speed of the prime mover, the system is adaptable for such a large change width and can realize the respective demanded actuator speeds.
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